The invention relates to the use of homopolymers and/or water-soluble copolymers of acrylic acid with one or more acrylic, vinyl or allylic monomers as dispersing agents for aqueous suspensions of calcium carbonate.
The invention also relates to the said aqueous suspensions of calcium carbonate and their uses in the fields of paper, like notably the manufacture or coating of paper, those of paint, fillers for synthetic resins and rubbers, detergent and cleaning formulations, and any other field using said suspensions such as notably ceramics, drilling fluids, cements, plasters and other fields of application in civil engineering and the construction industry.
For a long time already, persons skilled in the art have known about the use of grinding and/or dispersing agents for aqueous suspensions of mineral particles constituted by acrylic polymers and/or copolymers, of low molecular weight, totally or partially neutralized by various neutralizing agents (FR 2 603 042, EP 0 100 947, EP 0 127 388, EP 0 129 329 and EP 0 542 644).
Persons skilled in the art also know about the use of grinding and/or dispersing agents constituted by the fraction of acrylic polymers and/or copolymers whose specific viscosity is between 0.3 and 0.8 (patents FR 2 488 814, EP 0 100 948 and EP 0 542 643).
But these various types of grinding and/or dispersing agents of low molecular weight which make it possible to obtain aqueous suspensions of mineral particles refined and stable over time do not allow the putting back into suspension or redispersal in water of mineral particles, such as notably calcium carbonate, issuing from a mechanical and/or thermal reconcentration step following upon a step of wet grinding without the use of a dispersant and at low concentration in terms of dry matter. Such mineral particles, issuing from this mechanical and/or thermal reconcentration step following upon a step of wet grinding without the use of a dispersant, pose serious usage problems for persons skilled in the art who must disperse these mineral particles in the form of suspensions at very high concentration in terms of dry matter in order to be able to offer them to the user in a form which can be manipulated by said user.
Confronted with this problem, the Applicant then found, surprisingly, that the selection of homopolymers of acrylic acid and/or water-soluble copolymers of acrylic acid with one or more acrylic, vinyl or allylic monomers of a different and higher molecular weight than all the literature known to date teaches (and notably the patent application EP 0 850 685), makes it possible to put into aqueous suspension the mineral particles issuing from this mechanical and/or thermal reconcentration step following upon a step of wet grinding without the use of a dispersant and at low concentration in terms of dry matter.
By a step of wet grinding without the use of a dispersant, the applicant means a step of wet grinding without any dispersant but possibly with small quantities of flocculating agent up to 500 ppm.
Thus, one of the aims of the invention is the use of homopolymers of acrylic acid and/or water-soluble copolymers of acrylic acid with one or more acrylic, vinyl or allylic monomers of a molecular weight corresponding to a viscosity index with a value from 0.08 to 0.80, and preferentially from 0.20 to 0.60, as dispersing agents for aqueous suspensions of mineral particles issuing from a mechanical and/or thermal reconcentration step following upon a step of wet grinding without the use of a dispersant and at low concentration in terms of dry matter.
Similarly, another aim of the invention is to provide a dispersing agent for aqueous suspensions of mineral particles issuing from a mechanical and/or thermal reconcentration step following upon a step of wet grinding without the use of a dispersant and at low concentration in terms of dry matter.
An additional aim of the invention is to provide a method of putting said mineral particles into aqueous suspension using the selection of homopolymers of acrylic acid and/or water-soluble copolymers of acrylic acid with one or more acrylic, vinyl or allylic monomers of a molecular weight corresponding to a viscosity index with a value from 0.08 to 0.80, and preferentially from 0.20 to 0.60.
Another aim of the invention, besides those already mentioned, is to provide aqueous suspensions of refined mineral materials obtained by the aforementioned method, and characterised in that they contain from 0.1% to 2% by dry weight, and preferentially from 0.3% to 1.0% by dry weight, with respect to the dry weight of mineral material, of aqueous suspension dispersing agent according to the invention.
Finally, an additional aim of the invention concerns the use of these mineral aqueous suspensions in the fields of mass filling and coating of paper as well as those of paint, ceramics, drilling fluids, fillers for synthetic resins and rubbers, detergent and cleaning formulations, and any other field using said suspensions such as notably cements, plasters and other fields of application in civil engineering and the construction industry.
These aims are achieved by virtue of the use according to the invention of homopolymers of acrylic acid and/or water-soluble copolymers of acrylic acid with one or more acrylic, vinyl or allylic monomers of a molecular weight corresponding to a viscosity index with a value from 0.08 to 0.80, and preferentially from 0.20 to 0.60.
These homopolymers and/or copolymers result from the various known methods of radical polymerization using the polymerization initiators well known to persons skilled in the art such as, for example, hydroxylamine-based compounds or also using the polymerization initiators such as peroxides like notably hydrogen peroxide, tert-butyl hydroperoxide or the persalts like notably sodium persulphate, ammonium persulphate, potassium persulphate or analogues, or also sodium hypophosphite, hypophosphorous acid or again also phosphorous acid and/or their salts in the possible presence of metallic salts for example of iron or copper in a polymerization medium which can be water, methanol, ethanol, propanol, isopropanol, butanols, or their mixtures or also dimethylformamide, dimethylsulphoxide, tetrahydrofurane, acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, hexane, heptane, benzene, toluene, xylene, and possibly in the presence of molecular mass controllers also referred to as chain transfer agents such as notably mercaptoethanol, thioglycolic acid and its esters, n-dodecyl mercaptan, acetic, tartaric, lactic, citric, gluconic or glucoheptonic acids, 2-mercaptopropionic acid, thiodiethanol, halogenated solvents like carbon tetrachloride, chloroform, methylene chloride, the ethers of monopropylene glycol, or their mixtures and analogues.
These homopolymers and/or copolymers used as dispersing agents according to the invention result from the various aforementioned methods of radical polymerization of one at least of the monomers chosen from among acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, isocrotonic, aconitic, mesaconic, sinapic, undecylenic, angelic or canellic acid, and/or acrylamido methyl propane sulphonic acid in acid or partially neutralized form, or also from among acrylamide, methacrylamide, the esters of acrylic or methacrylic acids such as notably ethyl acrylate, butyl acrylate, methyl methacrylate, phosphate of acrylate or methacrylate of ethylene or propylene glycol or also again from among vinylpyrrolidone, vinylcaprolactame, isobutylene, diisobutylene, vinyl acetate, styrene, alphamethylstyrene, styrene sodium sulphonate vinylmethylether, or the allylics such as notably allylamine and its derivatives.
These homopolymers and/or copolymers used as dispersing agents according to the invention are partially or totally neutralized by one or more neutralizing agents having a monovalent function and possibly a polyvalent function.
The neutralizing agents having a monovalent function are chosen from the group constituted by the compounds containing alkaline cations, in particular sodium and potassium, or also lithium, ammonium, or again the aliphatic and/or cyclic primary or secondary amines such as for example the ethanolamines, mono and diethylamine or also cyclohexylamine.
The neutralizing agents having a polyvalent function are chosen from the group constituted by the compounds containing alkaline-earth divalent cations, in particular magnesium and calcium, or also zinc, and likewise by the trivalent cations, including in particular aluminium, or also by certain compounds containing higher-valency cations.
The homopolymers and/or copolymers designed to be used according to the invention as dispersing agents in water for mineral particles issuing from a mechanical and/or thermal reconcentration step following upon a step of wet grinding without the use of a dispersant and at low concentration in terms of dry matter are selected from among the homopolymers or copolymers having a molecular weight corresponding to a viscosity index with a value from 0.08 to 0.80, and preferentially from 0.20 to 0.60.
The molecular weight of the homopolymers or copolymers is measured on the form of the polymer salified with soda and according to the procedure described below and will be referred to as the viscosity index throughout the remainder of the present application.
To do this, the acid form of the compound whose viscosity index it is necessary to determine is 100% neutralized with soda and then diluted at 50 g/l in bipermutated water. This parent solution, which then has a concentration denoted c0, is subjected to the following dilutions: (2/3)c0, (1/2)c0, (1/3)c0, (1/4)c0, (1/6)c0, (1/12)c0, (1/18)c0, (1/24)c0, (1/36)c0.
The specific viscosity for each solution is then determined by means of a Schott AVS/500 viscometer equipped with an Ubbelohde tube of reference 53010/I and constant 0.01 and the specific viscosity curve is plotted as a function of the concentration.
The linear part of the curve makes it possible to obtain the viscosity index according to the equation
Viscosity index=Limit of the specific viscosity when the concentration tends to zero.
The refined mineral substances to be put into suspension according to the invention are chosen from among the synthetic calcium carbonates or the natural calcium carbonates such as notably chalk, calcite, marble or also dolomite or their mixtures.
Thus, the use according to the invention of a selection of homopolymers of acrylic acid and/or water-soluble copolymers of acrylic acid with one or more acrylic, vinyl or allylic monomers and the development of a dispersing agent according to the invention permits the putting into suspension of mineral substances issuing from a mechanical and/or thermal reconcentration step following upon a step of wet grinding without the use of a dispersant and at low concentration in terms of dry matter and thus allows the obtaining of aqueous suspensions of refined mineral materials obtained by the aforementioned method and containing said dispersing agent according to the invention.
In practice, the operation of dispersing or putting into aqueous suspension of said mineral substances consists of adding, under agitation, the necessary amount of dispersing agent according to the invention so as to obtain an aqueous suspension of said mineral materials, issuing from a mechanical and/or thermal reconcentration step, having a concentration in terms of dry matter of at least 60% with a Brookfield viscosity strictly less than 2000 mPa.s measured at 100 rpm immediately after the putting into suspension and a Brookfield viscosity strictly less than 20,000 mPa.s, measured at 10 rpm after eight days"" storage without agitation, that is to say so as to obtain an aqueous suspension of said mineral materials highly concentrated in terms of dry matter which remains able to be manipulated by the user even after a storage of a number of days and without agitation.